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ENGINEER DEPARTMENT, UNITED STATES ARMY. 



METHOD 



OF 



SINKING CRIBS, 



DEVISED BY 



D. C. HOUSTON, 

MAJOR OF ENGINEERS, BVT. COLONEL U. S. A. 



Printed for the nse of the Engineer Department, IT. S. A. 



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WASHINGTON, D. C. 
1874. 



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Section ihroiic/lh tine A.B. 





VLlAN 

of 

CRIB IN CHICAGO BREAKWATER 

Showing metlio d of sinking* 
devised V^ajor D.C.HOUSTON, Corps of Engineers 1T.S.A. 

1873. 

Engraved ia the Office of the Grief of Engineers. 



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PLAJ^ 

of 

CRIB m CHICAGO BREAKWATER 

Showing nietho d of sinking" 
devised tyMajor D.C.HOUSTON, Corps of Engineers U.S. A. 
1873. 

Eu|i'avcd iiL die Office uf die Chief of Engineers. 



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METHOD OF SINKING CRIBS, 

devised by d. c. houston, major of engineers, u. s. a. 

United States Engineer Office, 
Chicago, Illinois, October 28, 1874. 

General : 

I have the honor to transmit herewith drawings showing method of 
sinking cribs devised by me, with the object of preventing any settling or displace- 
ment of the cribs. 

Six piles are driven on each side of the site of the crib, in pairs, as shown in the 
drawing and perspective view. The piles are capped with a stick of oak timber, 
running the whole length of the crib. The crib is built in three compartments by 
partitions running lengthwise. The middle compartment has a close bottom, about 
13 courses below the top. The outer compartments have entirely open bottoms, or 
may have a single longitudinal stick, as shown in the drawing. In the cribs sunk at 
Chicago they are entirely open, which is considered preferable. Chains are attached 
to the lower cross timbers of the crib, three on each side. The chains are made of 
sufficient length to enable them to be securely fastened to the oak timber between 
each pair of piles, when the crib is lowered to its required position. The piles hav- 
ing been driven and capped, and the crib framed, the latter is lowered to its position 
and weighed down with stone, until its bottom is (say) four feet above the bottom 
of the lake. 

The chains are then secured to the oak timbers in the manner described. 

The upper end of the chain is provided with a hook which will pass through any 
link. 

It was found desirable to take two turns of the chain over the oak timber. This 
prevents any further settlement. The filling then proceeds, care being taken not to 
put too much stone in the middle compartment, to bring too great a strain on the 
chains until the outer compartments are filled. These outer compartments having 
open bottoms, allow the stone to pass through freely. Foundations are thus formed 



Is 



LIBRARY OF CONGRESS 



METHOD OF SINKING CRIBS. 




021 624 182 4 



on which the crib rests. In case of any undermining the stone passes down without 
taking the crib with it, and thus prevents any displacement or settlement of the crib. 
The stone in the middle compartment, which has a close bottom, does not move, 
and is sufficient to secure the crib in its place in case of storms, and prevents the 
possibility of the crib rising by the sifting of the stone through the grillage 
bottom, as has sometimes occurred. It is considered that the bottom of this middle 
compartment may be nearer to the top of the crib. 

The crib thus remains in the position in which it was originally placed, and the 
superstructure can be put on at once. Three cribs have been placed in this manner 
in the Chicago breakwater, and so far successfully. After a crib has been once placed 
and filled in this manner it is not seen how it can be displaced. 

This method is adapted to all soft or sandy bottoms, where there is a tendency to 
undermine. It ensures a close fit of the cribs, and a perfect alignment, and avoids 
the difficulties and expense of leveling up and otherwise arranging for the super- 
structure. 

This method has also the advantage of securing the crib during the process of sink- 
ing. The additional cost of the piles, &c, is more than compensated for in the di- 
minished amount of timber and stone required, and the reduced cost of putting on 
the superstructure. The superstructure need not necessarily be continuous. Addi- 
tional stone should be thrown in on each side of the crib. 

I am, General, 

Very respectfully, your obedient servant, 
D. C. Houston, 

Major of Engineers. 
Brig. Gen. A. A. Humphreys, 

Chief of Engineers, U. S. Army. 



